The age-related and T-independent properties, of Haemophilus influenzae type b capsular polysaccharide (Hib) and other polysaccharides of invasive organisms, limit their protective actions in infants and children, that age group which the highest attack rate of diseases due to these encapsulated pathogens. Organic synthetic schemes, that bound Hib and other capsular polysaccharides to tetanus toxoid, were devised in order to both increase the immunogenicity of and confer T-cell dependence (booster effect) to these protective antigens. Based upon ours, and others work in the field, a conjugated Hib vaccine, prepared by our original method, was licensed by the FDA for universal use in children older than 18 months of age. The safety and immunologic properties of our Hib-TT vaccine has been investigated in 18 month olds and now to two to three month old infants. The preliminary results show that protective levels of antibodies were induced in the young infants after two injections. Effectiveness study of this vaccine in infants and children in Charlotte, N.C. and Goteborg, Sweden are being planned.